Cylindrical cumulation of fast ions in a ring focus of a high-power subpicosecond laser

A new method of cylindrical cumulation of fast ions undergoing ponderomotive acceleration at the focus of a high-power subpicosecond laser is proposed. When a laser beam is focused in a preionized gas at a ring focus, radial acceleration of ions by the ponderomotive force occurs. The ions accelerated from the inner side of the ring form a cylindrical shock wave converging toward the axis. As the shock wave cumulates, the ion density increases rapidly and the ion-ion collision probability increases along with it. A numerical simulation for a ~100 TW subpicosecond laser pulse predicts the generation of up to 200 keV ions and up to 100-fold volume compression of the plasma in a cylinder ~1 µm in diameter. The lifetime of the dense plasma filament over the length of the laser caustic is several picoseconds. It is suggested that laser cumulation of ions be used for the production of a bright and compact subpicosecond source of fast neutrons, media for x-and γ-ray lasers, and multiply-charged ions and for the initiation of nuclear reactions.